The change in measured harmonics based on driver orientation is extremely small in any conceivable scenario when the discussion is outside measurements...aka ground plane. In terms of maximum output per CEA 2010....you would be looking at POSSIBLY a tenth of a single dB. I don't want to speak for Bill but I believe he may explain that the majority of the distortion change in his scenarios is due to high frequency absorption from carpeting. Even then, this is a VERY minor shift. If anyone thinks this can cause even a single decibel difference in CEA-2010 checks...you are off by magnitudes..

Tom V.
Power Sound Audio

“The bitterness of poor quality remains long after the sweetness of low price is forgotten" --- Ben Franklin

I don't want to speak for Bill but I believe he may explain that the majority of the distortion change in his scenarios is due to high frequency absorption from carpeting. Even then, this is a VERY minor shift. If anyone thinks this can cause even a single decibel difference in CEA-2010 checks...you are off by magnitudes..

If a sub is running an 80Hz fundamental at 100dB with 10% THD that's a lot of content at the 160Hz second and the 240Hz 3rd harmonics, and it's easily heard due to the effects of equal loudness. That's what a downfiring sub on carpet will help filter out. Even without carpet downfiring will acoustically filter at the higher harmonics. But it won't do anything to the 2nd, 3rd and 4th harmonics of a 20Hz fundamental that occur at 40, 60 and 80Hz..

And jbrown and the rest of you Canadians, you guys have a lot of cojones sticking the US with Bieber. What, Celine Dion wasn't enough for you?!

Thanks, America, for the Kardashians. 'nuff said.

Yeah, but we didn't send them up North! Never has an entire family owed so much to a daughter's sex tape. Unfortunately, TV programming is littered with these reality shows. Just like black mold in a flooded basement, they've spread to all channels.

"I've found that when you want to know the truth about someone that someone is probably the last person you should ask." - Gregory House

So, I believe that ShadyJ has overreached with this extrapolation thing.

I don't think I have over-reached there. Just take a look at the orientation comparison PA-150 measurements. When the woofer is facing the mic, measured port output drops by 4 dB, look at output around 20 Hz. When the port is facing the mic, bass from the woofer decreases by about 4 dB, just look at the upper bass range. Tom is assuming the best of both scenarios in his extrapolation.

Quote:

Originally Posted by Tom Vodhanel

Hi Chu,The change in measured harmonics based on driver orientation is extremely small in any conceivable scenario when the discussion is outside measurements...aka ground plane. In terms of maximum output per CEA 2010....you would be looking at POSSIBLY a tenth of a single dB.

I would think that the harmonic distortion contribution would be frequency dependent and intensity dependent for down firing vs forward firing. If you lost a decibel or two from measuring a down-firing orientation from a front-firing orientation, you are mostly losing upper bass output, and of course the harmonics will be primarily upper bass output. Let's say you have 10% THD at 80 Hz. If my math is right, losing a single decibel is about 10% of a signal. So if you have lost a decibel or two by measuring from a down-firing orientation, you have disproportionately lost distortion. How much exactly, I don't know, but I would guess a lot more than the fundamental. In light of this, I want to see how only a tenth of a decibel of distortion is affected? That stands to reason if we were talking about normal volume levels, but were are talking about CEA measurements where the driver is being pushed to its limit.

If a sub is running an 80Hz fundamental at 100dB with 10% THD that's a lot of content at the 160Hz second and the 240Hz 3rd harmonics, and it's easily heard due to the effects of equal loudness. That's what a downfiring sub on carpet will help filter out. Even without carpet downfiring will acoustically filter at the higher harmonics. But it won't do anything to the 2nd, 3rd and 4th harmonics of a 20Hz fundamental that occur at 40, 60 and 80Hz..

This looks like it could be a shortcoming of CEA 2010, it seemingly does not account for the equal loudness curve. The distortion thresholds are fixed:

This looks like it could be a shortcoming of CEA 2010, it seemingly does not account for the equal loudness curve. The distortion thresholds are fixed:
2nd harmonic: -10 dB.

Is that supposed to be dB or THD percentage? -10dB is horrid. If the signal is 80Hz at 80dB that would make the 160Hz harmonic 70dB, and factoring in equal loudness the 160Hz would as loud as the 80Hz.
OTOH 10% THD is -20dB. In that case the 160Hz harmonic wouldn't be heard as loud as the 80Hz signal, though it would still be far more audible than desirable, as it would be heard as half as loud.

That is dB from this article about it. I agree it is very lenient, and you can see this from some of the passing scores on data-bass.com: 30% THD of 20 Hz is passing grade?! That would be clear as a bell and a lot louder than the fundamental.

So if you have lost a decibel or two by measuring from a down-firing orientation, you have disproportionately lost distortion. How much exactly, I don't know, but I would guess a lot more than the fundamental. .

completely invalid argument according to yourself! a guess holds no merit....especially if it wasn't extrapolated

Jim and I have spent a few thousand hours outside, measuring hundreds of different products in just about every conceivable manner. Josh Ricci is well known in the industry as one of the most experiences folks around when it comes to outside measurements.

You can see in the post I made well over a YEAR ago...we measured the XV15 in multiple orientations. As my time here is very limited I'll try to make a few quick comments.

1)my comments regarding the effect of the driver facing in some direction OTHER than directly at the measurement mic are not guesswork or assumptions. My comments are based on 15 years of ground plane work. We measured the XV15 in this *exact* manner during the various stages of development(as we have with most/all of our proto types. I have formed my opinion on this issue based on all of the data at our disposal. The differences between the two orientations were very consistent. With the (center) of the driver moved to the 91 inch mark(down firing as Josh Ricci measured) the CEA-2010 scores *always* dropped as described in the thread I referenced above. So my opinion here isn't something I *hope* is true....it IS true based on well over a decade of data collection.

2)If the claim of distortion reduction by the driver facing down was a true influence on CEA-2010 scores Josh would obviously have made mention of this. And we would have also mentioned this too whenever the subject was discussed. The truth is this is *not* much of an influence. The majority of influence will be with harmonics >300hz. If you look at our data-bass testing you will see our CEA-2010 scores are almost all "amplifier limited" The "highest" harmonic that WAS a contributor (limiter) to the CEA-2010 scores of the XV15 is the "third harmonic" of 25hz....or 75hz. This frequency has a wave length of about 15 feet. This is too long to be altered in any significant fashion during GP work per the CEA-2010 guide lines. Can you see something on the order of a 0.05dB change(worst case)? Sure. How would this effect a 20-63hz CEA-2010 score? Maybe by 0.1dB...maybe. This is the type of influence a shift in the barometric pressure might have..

3)I dug up an old test sheet from the XV15 as Josh measured. This is from almost 2 years ago. The current XV15 used an improved driver and a DSP program that "loosens up" some of the limiters a bit.

Anyway, I certainly don't have the time to spend dodging the "bullet du-jour" from the anti-Tom coalition like this on a regular basis but I hope the above will offer a little information on how my opinion(s) have been formed over the last 15 years of measuring speakers and subwoofer.

So, I believe that ShadyJ has overreached with this extrapolation thing.

I don't think I have over-reached there. Just take a look at the orientation comparison PA-150 measurements. When the woofer is facing the mic, measured port output drops by 4 dB, look at output around 20 Hz. When the port is facing the mic, bass from the woofer decreases by about 4 dB, just look at the upper bass range. Tom is assuming the best of both scenarios in his extrapolation.

That's also a sub with the driver on the front face and the port on the rear. There's no way you can possibly orient the sub to get the two to point in the same direction. Now, if you took Tom's sub and rotated it 90 degrees, you'd also get substantially different numbers. To test Tom's premise that one can use a formula to account for the distance difference is to measure a front firing sealed sub. Then rig up some legs and 'convert it into a down firing sealed sub. Measure again. Apply the formula and see where it gets you.

"I've found that when you want to know the truth about someone that someone is probably the last person you should ask." - Gregory House

That is dB from this article about it. I agree it is very lenient, and you can see this from some of the passing scores on data-bass.com: 30% THD of 20 Hz is passing grade?! That would be clear as a bell and a lot louder than the fundamental.

Whether distortion is audible with respect to the fundamental is not easily answered. It depends on a numer of factors. For example, what's the order of the distortion? What frequency are we talking about? We're most sensitive to level changes in the 1-4 kHz region. Go up or down and we become progressively worse at hearing not only level changes but even detecting the signal. Does the distortion fall within the critical bandwidt? For low frequency content the critical bandwidth is on the order of 100 Hz. If the distortion products fal within the critical bandwidth, they can be quite high and still not be detected due to masking. Move to music or the content in movies, our discriminatory ability becomes even worse due to the nature of the program material which changes with time. These facors among others is what led to the distortion thresholds in the CEA specification. For a more in depth and better understanding of this, consider PM'ing Kal Rubinson who is eminently qualified in this area.

"I've found that when you want to know the truth about someone that someone is probably the last person you should ask." - Gregory House

These facors among others is what led to the distortion thresholds in the CEA specification. For a more in depth and better understanding of this, consider PM'ing Kal Rubinson who is eminently qualified in this area.

I don't get it. If someone buys sufficient woofage for home theater purposes.......doesn't all of this become moot? Some are posting as if it's common to drive their subwoofers to max capacity as opposed to dialing in their system flat and using their system like a person who values their purchase.

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To me, the discussion revolves around single subwoofer systems when most here have multiple subwoofer systems that can easily drive their rooms to full on reference sound levels, without breaking a sweat.

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My above is a sincere question as we purchased our subwoofer system as a pair, with the reasonable expectation of being able to obtain reference level playback, without tasking the system; lots of headroom; not playing close to max capability. My point, if one buys right, don't issues involving distortion in the form of THD, go by the wayside?

These facors among others is what led to the distortion thresholds in the CEA specification. For a more in depth and better understanding of this, consider PM'ing Kal Rubinson who is eminently qualified in this area.

I don't get it. If someone buys sufficient woofage for home theater purposes.......doesn't all of this become moot? Some are posting as if it's common to drive their subwoofers to max capacity as opposed to dialing in their system flat and using their system like a person who values their purchase.

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You're making a lot of assumptions. I'm just explaining to the best of my memory why the distortion limits are what they are. Some stick it in the only place that works, and so we go. Some dial it in flat, some think they have, some like it hot. Look at it (CEA) as one of the measures of performance.

Quote:

To me, the discussion revolves around single subwoofer systems when most here have multiple subwoofer systems that can easily drive their rooms to full on reference sound levels, without breaking a sweat.

...

Thats because we're talking about the measurement(s) as pertains to subs. There are people who look to achieve faithful playback to the low single digits.

Quote:

My above is a sincere question as we purchased our subwoofer system as a pair, with the reasonable expectation of being able to obtain reference level playback, without tasking the system; lots of headroom; not playing close to max capability. My point, if one buys right, don't issues involving distortion in the form of THD, go by the wayside?

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I think getting a handle on what the sub is capable of, how it behaves when pushed, etc. are useful things to know.

"I've found that when you want to know the truth about someone that someone is probably the last person you should ask." - Gregory House

Whether distortion is audible with respect to the fundamental is not easily answered. It depends on a numer of factors. For example, what's the order of the distortion? What frequency are we talking about? We're most sensitive to level changes in the 1-4 kHz region. Go up or down and we become progressively worse at hearing not only level changes but even detecting the signal. Does the distortion fall within the critical bandwidt? For low frequency content the critical bandwidth is on the order of 100 Hz. If the distortion products fal within the critical bandwidth, they can be quite high and still not be detected due to masking. Move to music or the content in movies, our discriminatory ability becomes even worse due to the nature of the program material which changes with time. These facors among others is what led to the distortion thresholds in the CEA specification. For a more in depth and better understanding of this, consider PM'ing Kal Rubinson who is eminently qualified in this area.

As for masking, I don't know of any studies that have been done demonstrating the audibility of deep bass harmonics on movie and music material. On sine waves it is very easy to hear, there is no question about that. Even 10% THD is easy to hear on deep bass tones.

CEA testing is very lenient IMO. That said, I'm thankful it exists at all. Let's face it, if it was much tougher, most of these companies would have blown it off and CEA would have been stillborn. I think that the authors were smart and that once everyone is all in, hopefully the standards will tighten up. It's one thing to scoff at a "new" testing procedure and another to skip an "established" one. Marketing genius to marketing nightmare. Give it a few more years and there should be more exposition.

CEA testing is very lenient IMO. That said, I'm thankful it exists at all. Let's face it, if it was much tougher, most of these companies would have blown it off and CEA would have been stillborn. I think that the authors were smart and that once everyone is all in, hopefully the standards will tighten up. It's one thing to scoff at a "new" testing procedure and another to skip an "established" one. Marketing genius to marketing nightmare. Give it a few more years and there should be more exposition.

CEA doesn't look like it has much of a future. Only a handful of sub makers would ever rely on CEA to sell their subs in the first place, because most subs are not output monsters. How many $1k subs can hit 115 dB at 2 m groundplane? The vast majority of subs are small and sold at places like bestbuy, so they are high on WAF and low on performance. Only among subwoofer enthusiasts will CEA ever be a thing. The broader audio market is going to ignore it totally. Only two publications are using it at all, Audioholics and Sound And Vision, so really only two guys are conducting CEA tests, Josh and Brent Butterworth. It doesn't help when you have companies like PSA who game the numbers which further drain them of meaning.

LOL. Shady you never cease to amaze me. Somehow you can always find a way to get a dig in against PSA in almost any post. It's almost an art form with you. I have to say, you are very dedicated to your agenda.

However, you do make a good observation about CEA. I hope Tack is right and you're wrong about it but you may very well be right, if all the manufacturers ignore it then who knows about it's future. But at least people like Josh can still run the tests and post results.

"The Data-Bass CEA-2010 results were within about a dB of PSA's own internal results and the other measurements corroborated each other well."

Quote:

Originally Posted by Hopinater

"LOL. Shady you never cease to amaze me. Somehow you can always find a way to get a dig in against PSA in almost any post. It's almost an art form with you. I have to say, you are very dedicated to your agenda."